Posted by: Graham Lee
on October 24, 2003 10:17 PM
Journaling filesystems have automatic rollback, which means they recover instantly from a crash.
Yeah, that'd be nice, wouldn't it? And much of the time it works; you can forget about 'init 0' and just hit the power switch. Well, that is my experience using ReiserFS, which is atomic so it may as well be an auditing FileSystem (and it has the performance hits associated therewith). My experience with ext3, which is just a metadata hack tacked onto the ext2 filesystem, is completely different. Turn the computer off, turn it back on, the thing tries to replay the journal, apparently succeeds, then if you're lucky will eventually get to a prompt, at which point a full fsck is required. However, if your / is ext3, this will be a single-user prompt. If you're unlucky, there will be unrecoverable data, and the system won't boot if it's something critical on<nobr> <wbr></nobr>/. I've had four power-cycles of a running system with the ext3 filesystem on some partition somewhere (and three of those were unplanned, one was a test); it managed to recover flawlessly on one, and recover after a fsck on one.
Your article suggests that a journalling filesystem is somehow a bullet-proof escape from dirty shutdowns. This just ain't so.
FOOTNOTE: BTW if you're thinking that maybe the disk with the ext3 partition on was broken in some way, that's not the case. I've done it on three different disks, two of which are still in use on my system with no problems and one of which is currently in someone else's firewall, again working just peachy.
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Posted by: Graham Lee on October 24, 2003 10:17 PMYeah, that'd be nice, wouldn't it? And much of the time it works; you can forget about 'init 0' and just hit the power switch. Well, that is my experience using ReiserFS, which is atomic so it may as well be an auditing FileSystem (and it has the performance hits associated therewith). My experience with ext3, which is just a metadata hack tacked onto the ext2 filesystem, is completely different. Turn the computer off, turn it back on, the thing tries to replay the journal, apparently succeeds, then if you're lucky will eventually get to a prompt, at which point a full fsck is required. However, if your / is ext3, this will be a single-user prompt. If you're unlucky, there will be unrecoverable data, and the system won't boot if it's something critical on<nobr> <wbr></nobr>/. I've had four power-cycles of a running system with the ext3 filesystem on some partition somewhere (and three of those were unplanned, one was a test); it managed to recover flawlessly on one, and recover after a fsck on one.
Your article suggests that a journalling filesystem is somehow a bullet-proof escape from dirty shutdowns. This just ain't so.
FOOTNOTE: BTW if you're thinking that maybe the disk with the ext3 partition on was broken in some way, that's not the case. I've done it on three different disks, two of which are still in use on my system with no problems and one of which is currently in someone else's firewall, again working just peachy.
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